1. Field of the Invention
The present invention relates generally to the construction of a medical appliance to be applied to a foot of a human patient for reduction of the risk of deep vein thrombosis (DVT). More specifically, it relates to a dual stage inflatable cuff that can be cycled intermittently to enhance blood circulation in a leg of a human patient.
2. Description of the Related Art
Therapeutic intermittent pneumatic compression of the leg for prevention of DVT after surgery has been used for many years, and a variety of devices have been developed for its application. Intermittent pneumatic compression is the technique of cyclically compressing the limb with air pressure so as to enhance circulation of blood. It has been shown effective in reducing the risk of thrombosis after surgery and for treatment of vascular deficiencies. Roberts et al., xe2x80x9cHemodynamics of Lower Limb in Man,xe2x80x9d Brit. J. Surg., Vol. 59, No. 3, pp. 223-226, March 1972, reports, for example, that intermittent pressure applied with an inflatable plastic splint causes an increase in venous peak flow directly proportional to the rate of pressure application, the venous peak flow being maximal at a pressure inflation rate of about 10 mmHg per second, with the maximum venous peak flow being reached when the intermittent pressure is applied at one minute intervals.
A system for applying therapeutic intermittent pressure to a limb is disclosed, for example, in U.S. Pat. No. 5,588,955 issued to Johnson, Jr. et al. and commonly assigned herewith, the disclosure of which is incorporated herein by reference in its entirety. The ""955 system generally comprises a pump, a reservoir which receives pressurized air from the pump, an inflatable cuff for sequentially applying pressure to the limb, means for intermittently and quickly transmitting pressurized air from the reservoir to the inflatable cuff, and pressure relief means operatively coupled to the inflatable cuff for limiting the pressure therein. In the operation of a preferred embodiment, the pump operates substantially continuously to supply a steady flow of pressurized air to the reservoir. The means for intermittently transmitting pressurized air from the reservoir to the inflatable cuff comprises a valve operatively disposed between the reservoir and cuff and a timer operatively coupled to the valve. The valve is normally in a closed position, so that pressurized air is allowed to build up in the reservoir to a level several times above that normally desired for therapeutic compression. The timer is set up to open the valve to release pressurized air from the reservoir to the inflatable cuff at predetermined intervals and for a predetermined duration. This results in a very rapid pressurization of the inflatable cuff which, in turn, leads to greater acceleration of venous flow and thus more effective therapy to the affected limb. The valve preferably is a two way valve so that when closed to the reservoir, it is open to atmosphere, allowing depressurization of the cuff.
Various constructions of inflatable cuffs are known in the art. For instance, the aforementioned ""955 patent discloses a cuff configured to apply pressure to only the medial and lateral aspects of the limb, leaving open the anterior and posterior aspects, such that collateral, rather than circumferential, compression is achieved. To this end, the cuff comprises a pair of semi-rigid shells intended to be disposed along the medial and lateral aspects of the limb, with one or both of the shells being provided with inflatable bladders along the inner surfaces thereof The shells are secured around the injured limb such that when the valve opens the bladders are pressurized and the semi-rigid shells resist such pressure so that all the pressure is directed to the interior of the limb.
It is also known that intermittent pneumatic pressure applied to the underside or sole of the foot is efficacious in the treatment of DVT in lower extremities of a patient. Thus, foot cuffs have been developed, such as the cuff disclosed in U.S. Pat. No. Re. 32,940 issued to Gardner et al. In the device disclosed in that patent, an inflatable air bladder is held against the arch of the foot by a sling. When inflated, the bladder tends to flatten the plantar arch causing a spread of the heel with respect to the ball of the foot and, therefore, necking down of involved blood vessels. Other patents relating to foot cuff devices include U.S. Pat. No. 4,614,180 issued to Gardner et al., U.S. Pat. No. Re. 32,939 issued to Gardner et al., U.S. Pat. No. 4,696,289 issued to Gardner et al., U.S. Pat. No. 4,702,232 issued to Gardner et al., U.S. Pat. No. 4,721,101 issued to Gardner et al., and U.S. Pat. No. 4,841,956 issued to Gardner et al. Prior art foot cuff devices include a device offered under the name PlexiPulse(copyright), by NuTech(copyright), a KCI company; a device offered by Huntleigh Healthcare of Manalapen, N.J.; and a device offered by Kendall under the name AV Impulse System.
One disadvantage associated with prior art devices that apply pressure only to the plantar arch is that such devices provide neither prevention nor treatment of edema of the forefoot. In fact, such prior art devices may even lead to increased edema of the forefoot by forcing some internal fluid from the center region of the foot distally to the forefoot.
Another problem associated with such known inflatable foot cuffs is that with considerable pressure being exerted against the foot in a localized area, counterforces are correspondingly generated at circumferentially spaced regions of the foot. These counterforces can be quite substantial, and can cause skin irritation and in some cases skin breakdown as a result of the cuff chafing the foot after repeated cycles of inflation and deflation. The resulting discomfort can significantly reduce patient compliance. In known cuff devices, such chafing is common on the top of the foot and in the heel region. One known foot cuff that attempts to address this problem is the inflatable foot cuff marketed by Huntleigh Healthcare company of Manalapen, N.J. In that device, open cell foam padding vented to the atmosphere is added to the straps and heel of the cuff in the areas of typical irritation. However, a disadvantage of such a construction is that the vented foam tends to compress and bottom out under pressure, rendering it of little benefit. Because compliance is an important aspect of efficacious foot cuff use, it is desirable, therefore, to provide a foot cuff construction that can be used over extended periods of time while minimizing chafing of the foot as occurs with present cuff constructions. It is further desirable to provide such a foot cuff construction that has an improved air pressure sequence due to the use of multiple separate air cells for increased compression effect on the affected foot and greater enhancement of blood flow in the affected limb.
The present invention improves over the prior art by providing an inflatable foot cuff for treatment of deep vein thrombosis including a generally flexible body member configured to envelop a foot of a human and having a central region adjacent to the sole of the foot when applied thereon. A larger inflatable air cell is disposed in the central region of the flexible body member, such that when the device is applied to the foot the larger air cell extends over at least the entire plantar arch of the foot and at least a portion of the forefoot distal of the plantar arch. A smaller separately inflatable air cell preferably is disposed within the larger air cell and distally in the vicinity of the forefoot. Intermittent sequential inflation of the smaller distal air cell followed by inflation of the larger air cell causes blood flow from the distal region of the foot to the proximal region of the foot and then up into the user""s leg, to enhance blood circulation in the leg. The compression of the forefoot provided by the device of the instant invention is also believed to be useful in the prophylaxis and treatment of forefoot edema. The body member is also provided with preinflated sealed air cells at counterforce pressure points to alleviate chafing and irritation of the skin when the foot cuff is operated.